1. Field of the Invention
The present invention relates to an injection molding machine, and more particularly to an injection molding machine having a molded article ejector in which an advancing stroke of an ejector rod can be set.
2. Description of Related Art
An injection molding machine is equipped with a molded article ejector that, after opening the mold, thrusts an ejector pin into the interior of the mold to eject the molded article adhering to the interior of the mold so as to remove the molded article from the mold. The molded article ejector advances ejector rods to push and advance an ejector plate provided inside the mold, so as to thrust an ejector pin provided on the ejector plate into the interior of the mold and eject the molded article from the interior of the mold.
The number of ejector rods that push the ejector plate that are mounted differs depending on the configuration of the mold, and therefore when changing molds it is necessary to make sure that the number of ejector rods matches the mold structure. If the configuration of the mold and the number of ejector rods do no match, the ejector rods will push the mold when the ejector rods advance after the mold is mounted and the molded article ejector could damage the mold.
In addition, there is a maximum advancing stroke of the ejector pin for each mold, and therefore the advancing stroke of the molded article ejector rods can be set for each mold. In a molded article ejector of this type, if there is an error in the value set for the advancing stroke of the molded article ejector rods and as a result the stroke is set beyond a permissible range, then when the molded article ejector rods are advanced they exceed a permissible stroke and attempt to move the ejector plate, and the ejector plate pushes the mold. As a result, the molded article ejector or the mold could be damaged.
Particularly in the case of an injection molding machine having a device that clamps the mold on a surface of a movable platen magnetically, since the mold is not clamped mechanically, the mold could fall when pushed by the ejector rods.
Conventionally, to confirm the ejection stroke, for example, a method is known that detects a state in which the molded article ejector can no longer advance, and that position is set as an advance limit position (see JP05-286001A). In addition, an invention is also known in which, during an initial advance, the molded article ejector is driven according to an advance operation pattern of set movement velocity and movement amount and the molded article ejected, with the advance operation pattern for the next and all subsequent advances determined on the basis of the final movement position obtained in this initial advance (e.g., JP09-254222A).
Moreover, an invention is also known that, in an injection molding machine that has a mold clamping device that mounts and clamps the mold on the fixed platen and the movable platen magnetically, by limiting a force with which the mold is opened (the mold is released) and the molded article ejected to a value that does not exceed a clamping force with which the mold is clamped to the movable platen, prevents the mold from separating from and falling off the movable platen due to the molded article ejecting force (JP2005-66856A).
As described above, mounting a number of ejector rods that does not match the configuration of the mold or using the wrong setting value for the amount of movement of the advancing stroke by the molded article ejector could damage the mold or the molded article ejector, or, if using a mold clamping device that mounts and clamps the mold magnetically, there is a risk that a force greater than the magnetic clamping force could be exerted on the mold by the molded article ejector and the mold could separate from and fall off the movable platen. As a result, when driving the molded article ejector, detecting the movement limit position of the advancing stroke, and determining a forward end position of the movement stroke of the molded article ejector rods (ejector pin) on the basis of that movement limit position as with the inventions described in JP05-286001A and JP09-254222A, since the movement limit position is set as the forward end position, this determined forward end position is not always optimal because, even in cases in which it is necessary to set a position further back as the forward end position and carry out molding, the movement limit position is set as the forward end position and molding is carried out. In addition, when the molded article ejector is driven when the mold is changed and one forgets to execute the operation of detecting the advancing stroke movement limit position, there is a risk that the mold or the molded article ejector may be damaged or that the mold may fall. Moreover, when using a mold clamping device that clamps the mold magnetically, with a method that sets the ejecting force to something less than the clamping force that clamps the mold to the moving platen, it is necessary to calculate the clamping force in advance. Consequently, if the calculation is erroneous, there is the same risk that the mold might fall. Furthermore, there is the problem that, if for some reason the magnetic clamping force changes, the set force must be revised.